HESITATION WHILE ACCELERATING

1998 Ford Ranger • 180,000 miles

I'm experiencing a hesitation while accelerating under a load. It usually occurs while I'm either in third or fourth gear at about 3000 rpms. If I let off the gas it will stop immediately. I seem to notice it more when cold, sometimes it drives perfectly. It has not thrown a CEL and doesn't have any codes stored. I've had it checked out by mechanics and they can't simulate the hesitation, but it happens to me all the time. It has new plugs, wires, and fuel filter. It also had upper and lower intake manifold gaskets replaced. I'm not sure what to try next.

The mechanics I've took it to checked the fuel pressure. They were happy with the reading. I've tried to look for other vacuum leaks. I sprayed carb cleaner around the engine and listened for any difference in idle. No difference. I haven't spotted any bad lines. Any particular ones I should look at?

Without being there, the only think I can think of is dealing with the ambient temp switch. IT tells the computer the coolant temp and from that, the computer adjusts fuel mixture. On a cold start, it could be running lean. Also, back to the compression. As steel heats up, it expands increasing compression. To confirm that isn't an issue, you may want to check it.

Okay I will do that. I drove the truck for a few hours today. It didn't make a difference whether the truck was cold or warmed up. Under loads or at freeway speeds it would buck and jerk. I couldn't power through it either. I'm getting worse gas mileage as well. Still no CEL.

You know, the "NO CEL" has me a bit confused. Usually if there is an electrical problem, a misfire, sensor issue. It shows up. I really question the fuel pump pressure. If there is an issue with the fuel pump, usually the CEL will not come on. Are you able to check it yourself? It could even deal with the fuel pressure regulator.

I checked the fuel pressure myself. 65psi running or off with key on. I have noticed that if I disconnect the battery an hook it back up my truck will run perfectly for a while before hesitating again.